最新提问
我的动态
登录后查看动态
题目内容双击单词支持查询和收藏哦～
A certain personal identification number (PIN) for opening garage doors is a sequence of 4 digits, where each digit is selected from the digits 0 to 9. How many such PINs have at least two different digits and are palindromes? (Note: A palindrome is a sequence of characters that reads the same backward and forward. For example, 1221 is a palindrome.)
B显示答案
· 相关考点
6.3.1 基本计数原理与加法原理
6.3.1 基本计数原理与加法原理
以上解析由 考满分老师提供。
